An Overview of the Impact of Dimming Metal Halide Discharge Lamps

A summary of the changes induced by operating metal halide discharge lamps below their rated power is presented. The changes for lamps, which operate under saturated dose conditions, are lowering of luminous efficacy, an increase in correlated color temperature, and a reduction in color-rendering properties. The impacts of these changes are reviewed with respect to the visual appearance of lighting installations, the reliability of lamps when operated for prolonged periods at reduced power, and some commercial consequences. The changes in output characteristics are much less marked if the lamp operates in an unsaturated dose regime.